Acoustic Path Research Articles

Automotive cabin acoustics and audio

We spend most of our quality listening time either at home or in a car. Unlike a concert hall -- where we spend the least amount of time listening, and on which there has been more than a century of research done -- there has very little research done for the home, and even less for the car. And this is why we put so much effort into the science of sound in homes and even more so into the science of sound in cars. Mr. Shively will explore the evolving path to becoming an audio engineer or an NVH engineer: the acoustic path. And, he will address the question of why sound quality does really matter, and the overlapping engineering disciplines which pursue sound quality. He will discuss how the audio systems are expanding to integrate Active Noise Control (ANC), Advanced Driver-Assistance Systems (ADAS), and Acoustic Vehicle Alert Systems (AVAS) for quiet car sound design and autonomous driver alerts in the pursuit of sound quality and how that is achieved. He will review the classical challenges of acoustics in a car and the new challenges for OEM audio system design and how they are being met. And, finally, he will touch on the evolution of expectations in automotive audio in existing markets and, more critically, emerging markets.

Scanning Doppler LIDAR wind profiles to inform near shore atmospheric acoustic propagation modeling

This work presents a comprehensive experimental system to measure concurrent atmospheric acoustic transmission loss and meteorological conditions. A three-dimensional scanning Doppler lidar wind profiler captures real-time wind speed gradients at many locations along the acoustic propagation path of a simple pitch catch style study. A long-range acoustic device on an anchored pontoon sends known chirp sequences to a seven-channel receiver array at the water’s edge at ranges up to approximately one kilometer. Additional synchronized meteorological observations include temperature, humidity, and wind measured with anemometers. The meteorological data stream is used to inform the sound speed gradient implemented in a parabolic equation based numerical model of atmospheric acoustic propagation. The model can account for sea surface roughness and accommodate a sound speed profile that changes along the propagation range. Model predictions are compared to measured transmission losses. An assessment of the value of the computational cost of incorporating the varying sound speed profiles in the model is presented.

Microphone vibration sensitivity: What it is, why it is important, and how to measure it

Microphones are designed to respond to acoustic pressure fields, but they can also be excited by external sources of mechanical vibration. In hearing aids, feedback is a difficult problem to resolve due to the high gain used to amplify sounds. The problem is worsened by the location of microphones and loudspeakers in close proximity, coupling both the acoustic and mechanical feedback paths. The first proposals of microphone vibration measurement techniques and definitional structure were published by Mead Killion in the 1970’s. Significant improvements in measurement technique have been published over the last 10 years. This talk will focus on a new measurement technique that allows for direct measurement of the “intrinsic vibration sensitivity”. The technique gives the ideal zero acoustic pressure condition at the microphone port and isolates room acoustic noise from the desired vibration signal. The noise floor of the new technique is 30 dB below previous methods, allowing for exceptionally clean measurement of primary-axis vibration sensitivity up to 10 kHz. Improvements are robust enough to enable the clean measurement of off-axis sensitivity of the microphone, which is often below 50 dBspl equivalent at 9.81 m/s2 of acceleration.

Robust processing for multipath in acoustic navigation, tomography, and source tracking

Because sound travels along many refracted paths through the ocean, passing through many horizontal sound speed layers, it is often challenging to unravel the received multipath to convert arrival times to ranges (e.g., by assigning them to eigenrays calculated by a ray tracer), particularly when it must be automated. This problem is exacerbated when the source and/or receivers are in motion. Assigning the wrong eigenray to an arrival results in the arrival time being modeled for the wrong acoustic path and the wrong range assigned to that arrival, resulting in degraded navigation, tomography, or localization. We will show how to take advantage of redundant measurements to ensure that we avoid spurious eigenray assignments. We use an initial “robust” optimization process whose cost function is less sensitive to spurious measurements or outliers than processes using least squared errors. Such processes both enable outliers to be identified and produce better estimates (than if spurious measurements were admitted). Better estimates allow the assignment of eigenrays to arrivals to be better constrained, often leading to corrected assignments. This virtuous cycle results in fewer spurious assignments and improved forward modeling for applications like navigation, tomography, and source tracking.

Sensing of ocean mixing via forward scattering acoustic scintillation

Ocean mixing process observations show complex spatio-temporal patterns as well as energy and dissipation levels that vary over six or more orders of magnitude, creating a challenging sampling problem. Acoustic imaging of ocean turbulent structures is informative, but extraction of quantities like spectra and dissipation rates of kinetic energy, ε, and temperature variance, Χ, requires geometric sampling constraints. Here, a remote sensing approach is proposed in the spirit of Di Iorio and Farmer (1994), and Duda et al. (1988), based on weak multiple-forward scattering physics. In the correct scattering regime, observations of the wavenumber spectrum of acoustic intensity obtained on a vertical array gives a direct measure of the range average turbulence index of the refraction spectrum in a plane transverse to the acoustic path. In this talk, the theory will be reviewed and some illustrative simulations will be presented; importantly, one-way acoustic transmission measures a combination of both ε and Χ. Experimental arrangements (frequency/range) where the theory is expected to apply will be outlined with an eye towards observing bottom boundary layer mixing. With a suitable vertical array, one could resolve scales from the smallest internal waves (∼several meters), through the transition regime, and down to scales of turbulence (∼tens of cm).

Signal Processing of Acoustic Data for Condition Monitoring of an Aircraft Ignition System

Degradation of the ignition system can result in startup failure in an aircraft’s auxiliary power unit. In this paper, a novel acoustics-based solution that can enable condition monitoring of an APU ignition system was proposed. In order to support the implementation of this research study, the experimental data set from Cranfield University’s Boeing 737-400 aircraft was utilized. The overall execution of the approach comprised background noise suppression, estimation of the spark repetition frequency and its fluctuation, spark event segmentation, and feature extraction, in order to monitor the state of the ignition system. The methodology successfully demonstrated the usefulness of the approach in terms of detecting inconsistencies in the behavior of the ignition exciter, as well as detecting trends in the degradation of spark acoustic characteristics. The identified features proved to be robust against non-stationary background noise, and were also found to be independent of the acoustic path between the igniter and microphone locations, qualifying an acoustics-based approach to be practically viable.

Ultrasonic imaging of buried defects in rails

The present work addresses the ultrasonic NDT of rails, more precisely of the rail foot. The practical constraint is that transducers must be located on the rail head, whereas the region of interest is the rail foot. Thus, there is no direct acoustic path between the transducers and the region of interest. As classical delay and sum methods cannot be applied to such cases, the goal of the paper is to numerically assess the potentiality of the topological imaging method to investigate the rail foot. Three specific typical rail foot defects are investigated, namely, longitudinal vertical cracks, corrosion pits and rail injuries. Simulating eight transducers with different polarizations, the images obtained show that the detection and approximate location of the various defects are possible.

Investigation of engineering models for sound propagation in a near-shore environment

This work presents an engineering approach to model the acoustic response of a sandy beach and its contribution to atmospheric sound attenuation of a near-shore acoustic source. Predictions of the sound pressure level at different ranges along the acoustic path are obtained with a parabolic equation solver that accounts for refraction and surface impedance variation along the propagation path. In this case study, sound propagates over flat water (126 m) and flat, smooth, sand (40 m). Experimental data are collected using a technique that uses chirp diversity to synchronize acoustic data with meteorological data. Sound pressure levels measured at the water’s edge and two range locations beyond the shoreline were compared to numerical results. Three models for acoustic behavior of sand were used to predict the sound pressure level at the beach. In particular, one of the models shows that transport properties of sand can be approximated by assuming sand grains are spherical particles. Generally strong agreement was found between predicted and measured sound pressure levels at the water’s edge. At 20 meters beyond the shoreline, modeling the beach with a reflective surface demonstrates an accuracy within 2 dB. When modeling the beach as a homogeneous absorber, none of the models proposed provided accurate results. However, when the sound absorption heterogeneity of the beach is accounted for using direct measurements of the effective flow resistivity, a better agreement (± 2 dB) was found at both 20 and 40 m beyond the shoreline. This work shows that good agreement between predictions and data can be also achieved by displacing the water–sand transition. Moving the transition to the location where the water saturation of the sand is below 10% and modeling the remaining beach with a semi-infinite layer of dry sand also produces agreement within 2 dB.

Acoustic wave propagation mechanism in the local stiffened structure of space station cabin using finite element method

Acoustic-based leakage detection and location in a spacecraft has attracted many researchers’ interest. Due to the fact that wave propagation through the stiffened structure is too complicated to be comprehensively understood, current leakage detection technologies have low-quality performance. Using numerical simulations, this paper parametrically investigates wave propagation across stiffened structure under different configurations. First, wave propagation through the stiffened structures with different stiffener heights is analyzed, showing that acoustic propagation features are different from Reusser’s model. Second, the stiffened structures with different widths are analyzed; meanwhile, the two cases of too large and too small stiffened ratios were compared. Acoustic wave propagation paths become complicated due to acoustic mode conversions. Third, different configurations of structure types are addressed. When the stiffener’s height–width ratio was large, the acoustic wave first reached the bottom of the stiffened block and then traveled up to the top of the stiffened block. When the stiffener’s height–width ratio was small, the acoustic wave reached the incident side at the bottom of the stiffened block and then propagated separately.

Self-balancing collaboration between linear and nonlinear adaptive sub-filters for hybrid active noise control

Conventional adaptive filters for active noise control (ANC) are troubled by the trade-off between convergence speed and steady state error, especially when nonlinearity plays an important role in system model. In this paper, a hybrid ANC algorithm called FBFLANN is constructed by the collaboration of FIR and bilinear functional link artificial neural network. The characteristics of linear and nonlinear sub-filters are analyzed and utilized to facilitate the adaptability in noise reduction. A convex factor is employed to automatically balance the contribution of two sub-filters, achieving faster convergence and higher accuracy in the presence of nonlinear distortions. The mathematical working and updating rules of the controller are derived to regulate the ANC process theoretically. The effectiveness of the proposed FBFLANN algorithm is demonstrated by numerous simulation studies considering diverse nonlinear acoustic path models as well as acoustic feedback interference. Hardware ANC platform is built up to verify the real-time noise control performance in physical noisy environments. The simulation and experiment results confirm the applicability and prospects for further development of the presented architecture in noise control scenarios.

Finite Element Analysis of the Distribution Parameters of a Metal Dot Array in a SAW Gyroscope

A surface acoustic wave (SAW) gyroscope has many unique advantages, but a low detection sensitivity limits its development. Previous studies have shown that adding a metal dot array to the acoustic wave propagation path of the SAW delay line can enhance the Coriolis force and further improve sensitivity. Therefore, in order to optimize the detection sensitivity performance of the sensor, 128°YX-LiNbO3, ST-X Quartz and X112°Y-LiTaO3 piezoelectric substrates were selected by finite element method to analyze the influence of the metal dot array size on the SAW gyroscopic effect in this paper. The most suitable metal dot size for 128°YX-LiNbO3 and X112°Y-LiTaO3 obtained by simulation are 5/16λ and 1/16λ, respectively; for example, when the normalized angular velocity is 1 × 10−3, the SAW gyroscopic effect factor g of the two piezoelectric substrates distributing the optimum size metal dots can reach 22.4 kHz and 5.2 kHz. For ST-X quartz, there is a threshold between the rotation speed of the substrate and the optimum size of the metal dot. When the rotating speed is lower than the threshold, the SAW gyroscopic effect is strongest when the metal dot size is 3/16λ; otherwise, the SAW gyroscopic effect is strongest when the size is 11/16λ. These research results provide new ideas for improvement of the SAW gyroscope.

Ultrasonic monitoring of the VVER-1000 FA form change

A procedure has been developed to determine the geometrical parameters of fuel assemblies (FA) by an ultrasonic pulse-echo technique used for all types of light-water reactor FAs. The measurement of geometrical parameters is achieved through the pairwise installation of ultrasonic transducers opposite the FA spacer grid faces at a distance of not more than a half of the transducer acoustic field near-region length such that the acoustic axes of the pairwise transducers are parallel to each other. The advantages of the presented technique is that it enables monitoring of any FA modifications, including the VVER reactor assemblies with a different number of spacer grids. The paper presents a mathematical model of the acoustic path developed in a geometrical acoustics approximation and its verification results. The model was used for computational and experimental studies of the ultrasonic test technique, and engineering formulas have been developed to calculate the errors of the transducer-measured distance to the FA surface. A code has been developed to simulate the FA form change monitoring and can be used to design new monitoring systems. The developed technique to determine the VVER-1000 FA geometrical parameters was introduced at units 1 and 2 of the Temelin NPP, the Czech Republic, for the TVSA-T FA form change monitoring. The successful use of the proposed technique makes it possible to recommend it for use in inspection benches at other NPPs.

Acoustical impacts on hard disk drive dynamics

Acoustical output from air movers in computing systems can reach sufficiently high sound pressure levels and in frequency bands such that performance of Hard Disk Drives (HDD) is degraded. In this paper air mover acoustical characteristics and comparisons to standalone measurements and models relevant to the performance issues are explored. Sound pressure levels, frequency bands, directivity, and explicit source descriptions are considered for air mover sources, and duct transmission, statistical energy, acoustic diffusion, and measured transfer factors are considered for noise transmission along acoustic path(s) from air mover to HDD within computing systems.

A multi‐step method for passive broadband source localisation using a single vector sensor

In the deep ocean, a vector sensor is deployed near the seabed to receive direct waves from the reliable acoustic path (RAP). In the space domain, the vector sensor can estimate the vertical arrival azimuth of the signal, which is sensitive to distance. In the frequency domain, the periodic interference pattern formed by the direct and surface-reflected wave is decided by both the source depth and the vertical arrival azimuth. In this work, a multi-step method for passive broadband source localisation using a single-vector sensor (SVS) is proposed. At first, the depth is estimated by the interference pattern in the frequency domain. Then the ranging problem is solved based on the depth estimated result. The impact of the surface-generated noise is considered. Compared with the scalar vertical line array (VLA) in simulation, the localisation performance of SVS has higher requirements for the signal-to-noise ratio (SNR) but is much smaller in size. In the experiment, Gaussian white noise from 310 to 430 Hz was emitted to simulate the underwater target. Compared with traditional match-field processing (MFP), the multi-step method is much more stable, accurate, and efficient. The computing time is drastically shortened.

Health Monitoring of Plate Structures Based on Tomography With Combination of Guided Wave Transmission and Reflection

Corrosion and damage occurring in the metallic structure threaten the normal operation of instruments and systems. Timely inspection of corresponding components are quite significant to spot the damages. The ultrasonic guided wave inspection technique has become a powerful solution to quantify and image the structural defect. This work proposes a novel tomography scheme to comprehensively utilize guided wave transmission and reflection, which facilitates the imaging performance. To achieve this goal, the disperse Lamb wave is adopted and omni-directional electromagnetic acoustic transducer is introduced. The bent acoustic ray model forms the base of the proposed method. The acoustic paths are obtained by the ray tracing technique according to the time of flight of received transmission wave and reflection wave. Further, the slowness distribution is reconstructed and it can be transformed to the thickness distribution. The case from simulation firstly validates the feasibility of this proposed method. In addition, the complicated case is set in the experimental section and the comparison with tomography from only transmission wave is conducted. The quantitative merits are also designed to measure the depth error and global error. The results of comparisons demonstrate the superiority of proposed scheme. Therefore, this scheme could be an alternative approach for better damage reconstruction.

Marine compressed air source array primary acoustic field characterization from at-sea measurements.

The primary acoustic field of a standard seismic survey source array is described based on a calibrated dataset collected in the Gulf of Mexico. Three vertical array moorings were deployed to measure the full dynamic range and bandwidth of the acoustic field emitted by the compressed air source array. The designated source vessel followed a specified set of survey lines to provide a dataset with broad coverage of ranges and departure angles from the array. Acoustic metrics relevant to criteria associated with potential impacts on marine life are calculated from the recorded data. Sound pressure levels from direct arrivals exhibit large variability for a fixed distance between source and receiver; this indicates that the distance cannot be reliably used as a single parameter to derive meaningful exposure levels for a moving source array. The far-field acoustic metrics' variations with distance along the true acoustic path for a narrow angular bin are accurately predicted using a simplified model of the surface-affected source waveform, which is a function of the direction. The presented acoustic metrics can be used for benchmarking existing source/propagation models for predicting acoustic fields of seismic source arrays and developing simplified data-supported models for environmental impact assessments.

Modified Model of Sound Velocity with Different Saturation in Fractured Sandstone

The hazards of surrounding rock sheeting, collapse and rock explosion during the excavation of underground projects can be regarded as the macroscopic dynamics of the evolutionary development of their internal fractures, mostly accompanied by acoustic emission phenomena. The application of acoustic emission detection technology can quickly determine the existence of fissures in the surrounding rock and predict their approximate location and spatial spread. Therefore, considering the effect of fissures on the sound velocity propagation law. In this work, experiments on the identification of acoustic emission signal paths in solid media with different void states are carried out, and the path propagation law of acoustic emission signals is explored and studied. A comparative analysis of acoustic emission source localization in fractured sandstone with different sensor arrays at different saturation levels was carried out using water as the coupling agent. The acoustic emission source 3D localization results are optimized by correcting the time difference model. The results show that the acoustic emission signal propagation conforms to the shortest distance principle. In the localization of 3D cylindrical AE sources, it is suitable to select a combined array of spatial tetrahedral sensors for better localization. As the saturation increases the positioning effect gets closer to the actual value. The sound source localization effect of the sound velocity correction model based on the time difference method is closer to the actual lead break position. In actual engineering, water as a benign coupling agent can better improve the accuracy of AE source localization in fracture-containing sandstone, which can provide some guiding suggestions for related engineering.

The Resulting Effect of Flow Pulsations on Calibration Constant of Acoustic Path in Ultrasonic Flowmeters.

The present paper compares, for the first time, the regimes of a pulsating turbulent flow in a smooth pipe in terms of 0.001 ≤ ω+ ≤ 0.0346 and 0.16 ≤ β ≤ 0.63 at Re ≈ 7000 with the uncertainty in estimating the flow rate by an ultrasonic flowmeter. It was revealed that the classification of pulsating flow regimes according to the dimensionless angular frequency ω+ does not have a direct relation with the K parameter equal to the ratio of the phase-average calibration constant in pulsating flow to the corresponding value in steady flow. The results of data processing showed that K depends on the relative amplitude of pulsations β and the position of the chord of the ultrasonic beam trajectory (L/R is distance L from the pipe center to the chord to the pipe radius R). In the coordinates β and L/R, there is a rather wide area where the uncertainty in flow rate estimation of pulsating flows should not exceed 0.5%. An increase in β or L/R leads to an increase in measurement uncertainty, which in the limiting case β, L/R → 1 can reach 5% or more. Favorable and unfavorable areas of the pipe section were identified when scanning pulsating flows and the effectiveness of using multi-path scanning schemes was estimated to reduce the resulting effect of flow pulsations on flow measurement uncertainty.

Model of the acoustic path of a separatecombined optical-acoustic transducer

Ultrasonic testing methods occupy one of the key positions in flaw detection, structurescopy, in assessing the strength characteristics of materials and the stress-strain state of products. The method is based on the phenomenon of acoustoelasticity and makes it possible to control the stress-strain state of products by changing the propagation velocity of a longitudinal subsurface ultrasonic wave. To excite acoustic waves, a separate-combined optical-acoustic transducer and a laser-ultrasonic flaw detector are used. The design of a separate-combined optical-acoustic transducer should ensure the measurements accuracy of the time it takes for a longitudinal subsurface wave to reach the receiver of acoustic oscillations. To analyze the recorded acoustic signals and extract from them the signal of a longitudinal subsurface wave, in this work, a finite element model of the acoustic path of a dual-coupled optical-acoustic transducer is proposed and developed. The finite element model was implemented in the COMSOL Multiphysics software package using an explicit solver based on the discontinuous Galerkin method. The developed finite element model makes it possible to visualize the displacement fields of acoustic oscillations, obtain A-scans, and calculate the time of arrival of a longitudinal subsurface wave at the receiver of the optical-acoustic transducer. The calculated values of the arrival time of a longitudinal subsurface wave at the receiver of an optical-acoustic transducer are compared with the results of a full-scale experiment. Calculations and full-scale experiments were performed for steel plates of various thicknesses. The adequacy of the model was confirmed using the Fisher criterion (F-measure). The A-scans obtained as a result of the simulation made it possible to identify the signals recorded by the optical-acoustic transducer: the signal of the longitudinal subsurface wave, the signals of the head and reflected transverse waves, and the intrinsic noise of the optoacoustic transducer. The developed model makes it possible to single out the signal of the longitudinal subsurface wave among the recorded signals of the optical-acoustic transducer. The proposed model can be used in the design of new optical-acoustic transducers, as well as in non-destructive testing (NDT) and materials science.

Target depth estimation by deep neural network based on acoustic interference structure in deep water

Automatic and robust target depth estimation is an important issue of an active detection system working in the reliable acoustic path (RAP) environment. In this paper, the target depth-sensitive acoustic interference structure is used as input, and a deep neural network (DNN) method is proposed to realize automatic depth estimation. Furthermore, to improve the robustness of the network, both the sound speed profile (SSP) uncertainty and the target trajectory uncertainty are considered in the training dataset. The former is modelled as a random weighted sum of the empirical orthogonal function (EOF), and the latter is modelled by the partial-data-lacking of the network input. The method was evaluated through simulated data and compared with the conventional method of matching the measured interference structure with the replicas. The presented method exhibits a higher accuracy of depth estimate in uncertain environments when the signal-to-noise ratio (SNR) is higher than −6 dB, but its performance deteriorates rapidly as the SNR decreases further. The method is also verified by semi-simulation with experimental data in deep water.